Soft detection of multichip DPSK over the nonlinear fiber-optic channel

We analyze the performance of a recently proposed multichip differential phase-shift-keying (DPSK) format over the nonlinear fiber-optic channel. For a single wavelength nonlinear phase-noise-limited channel, a multichip DPSK receiver based on a three-chip observation can attain more than two orders of magnitude bit-error-rate reduction relative to a standard DPSK receiver, or equivalently ∼1-dB improvement in Q-factor, significantly exceeding the 0.2-dB improvement achieved by the same format over a linear optical channel.